Protection device and imaging device

Abstract

This protection device comprises: a clamp element connected to a high voltage line; a capacitor connected between the clamp element and a low voltage line; and a resistor connected in parallel with the capacitor, between the clamp element and the low voltage line.

Description

Protective device and imaging device

[0001] The present technology relates to a protection device and an imaging device, and in particular to protection against surge voltages.

[0002] For example, as disclosed in Patent Document 1, an overvoltage protection circuit has a TVS (Transient Voltage Suppressor) diode as a clamping element, and when an overvoltage is input, a current flows through the clamping element, thereby clamping the voltage and preventing the overvoltage from being applied to a subsequent stage.

[0003] Japanese Patent Application Laid-Open No. 2022-53886

[0004] The technology disclosed in Patent Document 1 includes a switch element that cuts off current flow, and a latch circuit that switches the switch element between a current-carrying state and a cut-off state. The latch circuit switches the switch element between a current-carrying state and a cut-off state, thereby preventing the clamp element from remaining current-carrying for a long period of time when an overcurrent occurs.

[0005] However, this latch circuit is composed of a power supply, three transistors, and seven resistors, which makes the configuration complicated and increases the size of the entire device.

[0006] The present technology has been made in view of the above circumstances, and aims to suppress damage to a clamp element in the event of an overvoltage with a simple configuration.

[0007] A protection device according to the present technology includes a clamp element connected to a high-voltage line, a capacitor connected between the clamp element and a low-voltage line, and a resistor connected in parallel with the capacitor between the clamp element and the low-voltage line. When an instantaneous surge voltage is input, charge is stored in the capacitor, causing a current to flow through the clamp element and limiting the voltage to the clamp voltage, and when a steady overvoltage is input, charge is stored in the capacitor, making it difficult for electricity to flow through the clamp element.

[0008] 4 is a diagram showing the configuration of a protection device; FIG. 5 is a diagram explaining surge voltage; FIG. 6 is a diagram showing voltage changes when a surge voltage is input; FIG. 7 is a diagram showing voltage changes when a steady overvoltage is input; FIG. 8 is an enlarged view of the dashed line portion in FIG. 4; FIG. 9 is a diagram showing the configuration of an input unit of an imaging device of a first example; and FIG. 10 is a diagram showing the configuration of an input unit of an imaging device of a second example.

[0009] Hereinafter, with reference to the accompanying drawings, an embodiment of a sensor device according to the present technology will be described in the following order: <1. Circuit configuration of protection device> <2. Configuration of imaging device> [2.1. Configuration of imaging device according to first example] [2.2. Configuration of imaging device according to second example] <3. Modification> <4. Summary of embodiment> <5. Present technology>

[0010] 1. Circuit Configuration of Protection Device> Fig. 1 is a diagram showing the configuration of a protection device 1. As shown in Fig. 1, the protection device 1 according to this embodiment includes a positive terminal 2 and a negative terminal 3. The positive terminal 2 and the negative terminal 3 are configured by, for example, connectors, and a specified DC voltage is supplied from an external power source. The DC voltage supply source (external power source) is assumed to be an AC adapter or a battery.

[0011] The positive terminal 2 is connected to a high voltage line 4, and the negative terminal 3 is connected to a low voltage line 5. In this embodiment, the low voltage line 5 is a reference ground line of 0 V (zero volts). In the following description, the positive terminal 2 side of the high voltage line 4 is referred to as the upstream side, and the side away from the positive terminal 2 is referred to as the downstream side.

[0012] A ferrite bead 6 and a ferrite bead 7 are connected in parallel to the high voltage line 4. The ferrite bead 6 and the ferrite bead 7 attenuate or block electrical noise from an external power supply.

[0013] Capacitors 8 and 9 are connected in parallel between the low-voltage line 5 and the downstream side (opposite side from the positive terminal 2) of the position where the ferrite beads 6 and 7 are provided on the high-voltage line 4. The capacitors 8 and 9 smooth the DC voltage input from the positive terminal 2.

[0014] A reverse connection protection FET 10 configured as a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is connected downstream of the position where the capacitor 9 is connected to the high-voltage line 4. The drain of the reverse connection protection FET 10 is connected to the positive terminal 2 via ferrite beads 6 and 7.

[0015] Resistors 11 and 12 are connected in series between the source side (downstream side) of the reverse connection protection FET 10 on the high voltage line 4 and the low voltage line 5. In addition, a capacitor 13 is connected between the downstream side of the position where the resistor 11 is connected on the high voltage line 4 and the connection point of the resistors 11 and 12. The gate of the reverse connection protection FET 10 is connected to the connection point of the resistors 11 and 12. In other words, the resistor 11 and capacitor 13 are connected in parallel between the source and gate of the reverse connection protection FET 10.

[0016] When DC voltage is normally input to the positive terminal 2 and the negative terminal 3, the reverse connection protection FET 10 turns on due to the potential difference between the source and gate of the reverse connection protection FET 10, and current flows downstream through the reverse connection protection FET 10. Note that at the moment when the power supply voltage is input to the protection device 1, no charge is stored in the capacitor 13, so no sufficient potential difference occurs between the source and gate of the reverse connection protection FET 10. Therefore, immediately after the power supply voltage is input, the reverse connection protection FET 10 remains in the off state until the capacitor 13 is fully charged. In this transient state, current flows through the parasitic diode 14 of the reverse connection protection FET 10. When current flows through the parasitic diode 14, charge begins to accumulate in the capacitor 13. Then, when a predetermined charge accumulates in the capacitor 13 and the potential difference between the two poles of the capacitor 13 becomes greater than a predetermined value, the reverse connection protection FET 10 turns on.

[0017] On the other hand, when the power supply voltage is input with reverse polarity to the positive terminal 2 and the negative terminal 3, no potential difference occurs between the gate and source of the reverse connection protection FET 10, so the reverse connection protection FET 10 is turned off. Therefore, when the external power supply is connected with reverse polarity, no current flows through the protection device 1. In this way, the reverse connection protection FET 10 functions as a switching element, thereby protecting the circuit when the external power supply is connected in reverse.

[0018] A surge protection circuit 15 is connected between the low-voltage line 5 and the high-voltage line 4 downstream of the position where the capacitor 13 is connected. Furthermore, an electronic component 16 to which the power supply voltage is supplied is connected downstream of the surge protection circuit 15 on the high-voltage line 4 and the low-voltage line 5. In practice, an overcurrent protection circuit against overcurrent and an overvoltage protection circuit against overvoltage are provided between the surge protection circuit 15 and the electronic component 16, and these protection circuits protect the electronic component 16 in the event of an overcurrent due to a short circuit or the like or a steady overvoltage being input. Furthermore, although the electronic component 16 is shown as a single block in the figure, it is actually made up of a plurality of electronic components.

[0019] The surge protection circuit 15 includes a clamp element 21, a capacitor 22, and a resistor 23. The clamp element 21 is configured by, for example, a TVS (Transient Voltage Suppressor) diode or a Zener diode. The cathode of the clamp element 21 is connected to the high-voltage line 4. The capacitor 22 and the resistor 23 are connected in parallel to the anode of the clamp element 21.

[0020] The capacitor 22 and the resistor 23 have one end connected to the anode of the clamp element 21 and the other end connected to the low voltage line 5 .

[0021] When the voltage on the cathode side becomes equal to or higher than the clamp voltage relative to the voltage on the anode side, clamp element 21 clamps the voltage and allows current to flow from high voltage line 4 to low voltage line 5, thereby limiting the potential difference between high voltage line 4 and low voltage line 5 to the clamp voltage. On the other hand, when the voltage on the cathode side is lower than the clamp voltage relative to the voltage on the anode side, clamp element 21 does not allow current to flow from high voltage line 4 to low voltage line 5.

[0022] Here, the clamp element 21 is provided to protect the electronic components 16 and the like by limiting an instantaneous overvoltage (hereinafter referred to as a surge voltage) input from an external power source to a clamp voltage. On the other hand, when a steady overvoltage is input, the above-described overvoltage protection circuit protects the electronic components 16 and the like. Note that an overvoltage is a voltage that is greater than a specified voltage. Furthermore, a steady overvoltage refers to an overvoltage that lasts for a longer period of time than a surge voltage.

[0023] Therefore, if the steady-state overvoltage is greater than the clamp voltage, a current will flow through the clamp element 21. If the capacitor 22 and resistor 23 are not provided as in this embodiment, a steady-state overvoltage flowing through the clamp element 21 may cause the clamp element 21 to heat up and be thermally destroyed. Therefore, if the capacitor 22 and resistor 23 are not provided as in this embodiment, the clamp voltage must be greater than the steady-state overvoltage input from the external power supply, and the withstand voltage of the electronic component 16 must be greater than the clamp voltage. However, because the clamp voltage of the clamp element 21 varies depending on individual devices, it is difficult to satisfy these conditions.

[0024] Therefore, the surge protection circuit 15 of this embodiment is equipped with a capacitor 22 and a resistor 23 in addition to the clamp element 21, thereby making it possible to prevent thermal destruction of the clamp element 21 even when the above conditions are not met, in other words, when a steady overvoltage is input to the clamp element 21.

[0025] The operation of the surge protection circuit 15 when a surge voltage and a steady overvoltage are applied will be described below.

[0026] FIG. 2 is a diagram illustrating surge voltage. Note that FIG. 2 is a graph of the voltage and current when a surge voltage is input without the surge protection circuit 15. In FIG. 2, the potential difference between the ferrite bead 6 and capacitor 8 on the high-voltage line 4 and the low-voltage line 5 is designated as voltage V1 (see FIG. 1). Also, the current upstream of the reverse connection protection FET 10 on the high-voltage line 4 is designated as current I. Also, in FIG. 2, the horizontal axis represents time, and the vertical axis represents voltage or current. Note that this also applies to the following figures.

[0027] As shown in Figure 2, assume that at time T1, an active external power supply is connected to the positive terminal 2 and the negative terminal 3. Then, as time passes, the current I increases and the voltage V1 also gradually increases, until the voltage value suddenly rises towards time T2. Then, at time T2, the voltage V1 becomes a surge voltage that exceeds the clamp voltage of the clamp element 21. Because the surge voltage is instantaneous, after time T2, the voltage V1 suddenly drops and finally reaches the specified voltage.

[0028] 3 is a graph showing voltage changes when a surge voltage is input, which is a graph of voltage and current when a surge voltage is input when the surge protection circuit 15 is provided.

[0029] 3, assume that at time T11, an active external power supply is connected to the positive terminal 2 and the negative terminal 3. Then, as time passes, the current I increases and the voltage V1 gradually increases, until it suddenly rises at time T12. When the voltage V1 reaches the clamp voltage of the clamp element 21 at time T12, the surge protection circuit 15 clamps the voltage V1 to the clamp voltage.

[0030] At this time, since the surge protection circuit 15 is provided with the capacitor 22, an electric charge is stored in the capacitor 22, which allows an instantaneous current to flow through the clamp element 21. Therefore, in the clamp element 21, a current flows from the cathode side to the anode side, and the current flowing through the clamp element 21 stores an electric charge in the capacitor 22.

[0031] The capacitance of capacitor 22 is set to a value greater than the amount of charge stored when a surge voltage is input and a current flows through clamp element 21. Therefore, even when a surge voltage is input, a charge exceeding the capacitance of capacitor 22 is not input from clamp element 21, and it is also possible to prevent current from ceasing to flow through clamp element 21.

[0032] As a result, in the surge protection circuit 15, when a surge voltage is input, the clamp element 21 limits the voltage V1 to the clamp voltage, thereby making it possible to protect the electronic component 16.

[0033] Figure 4 shows voltage changes when a steady overvoltage is input. Figure 5 is an enlarged view of the portion surrounded by the dashed line in Figure 4. Figures 4 and 5 are graphs of voltage and current when a steady overvoltage is input when a surge protection circuit 15 is provided. In Figures 4 and 5, the potential difference between the capacitor 13 and the surge protection circuit 15 on the high-voltage line 4 (downstream of the reverse connection protection FET 10) and the low-voltage line 5 is designated as voltage V2. The potential difference between the two electrodes of capacitor 22 is designated as voltage V3.

[0034] 4 and 5, assume that at time T21, an active external power supply is connected to the positive terminal 2 and the negative terminal 3. Then, as time passes, the current I increases and the voltages V1 and V2 gradually increase, until they suddenly rise towards time T22. Then, at time T22, the voltages V1 and V2 become the clamp voltages of the clamp element 21, and the voltages V1 and V2 are clamped to the clamp voltages.

[0035] At this time, current flows from the cathode side to the anode side of clamp element 21, and the current flowing through clamp element 21 accumulates charge in capacitor 22. However, if a steady overvoltage is input, charge gradually accumulates in capacitor 22, and as shown in Figure 4, the voltage V3 between the electrodes of capacitor 22 gradually increases over time. When the amount of charge accumulated in capacitor 22 reaches its capacitance, capacitor 22 can no longer accumulate any more charge, and the current flowing from high-voltage line 4 through clamp element 21 to capacitor 22 almost stops.

[0036] However, the current passing through clamp element 21 does not completely stop, but continues to flow slightly through resistor 23 even after the charge stored in capacitor 22 has become capacitance. The resistance value of resistor 23 is set to a value that will prevent clamp element 21 from being thermally destroyed by the current flowing through clamp element 21 when a steady overvoltage is input. Therefore, even if a small amount of current flows through clamp element 21 after the charge stored in capacitor 22 has become capacitance, clamp element 21 will not be thermally destroyed.

[0037] After a surge voltage or steady overvoltage is input, when the input of this voltage ends, current stops flowing through clamp element 21 to capacitor 22 and resistor 23. Then, the resistance value of resistor 23 is set to a value that allows the charge stored in capacitor 22 to be discharged, so the charge stored in capacitor 22 flows to low-voltage line 5 via resistor 23. As a result, even if a surge voltage or steady overvoltage is input, the charge in capacitor 22 is eventually discharged, making repeated use possible.

[0038] As described above, the surge protection circuit 15 can protect the electronic component 16 from surge voltages and prevent thermal damage to the surge protection circuit 15 even when a steady overvoltage is input, with a simple configuration including the clamp element 21, the capacitor 22, and the resistor 23. Furthermore, the surge protection circuit 15 only needs to set the clamp voltage of the clamp element 21 below the withstand voltage of the electronic component 16, and does not need to set the clamp voltage of the clamp element 21 higher than the steady overvoltage. This makes it possible to prevent damage due to variations in the clamp element 21 due to individual differences. Furthermore, the selection of the clamp element 21 does not need to be strict, making it easier to select the clamp element 21. Furthermore, since the surge protection circuit 15 can be used with multiple types of external power supplies, it can accommodate a wide range of external power supplies.

[0039] 2. Configuration of Imaging Device 2.1. Configuration of Imaging Device of First Example Next, a description will be given of the configuration of the input section of an imaging device including the protection device 1. Fig. 6 is a diagram showing the configuration of the input section of the imaging device 30 of the first example. As shown in Fig. 6, the imaging device 30 of the first example includes, in addition to the protection device 1 (surge protection circuit 15), a DC-IN connector 31, an overcurrent detection circuit 32, a voltage detection circuit 33, a cutoff switch 34, and a step-down power supply circuit 35.

[0040] In the imaging device 30, a DC-IN connector 31, a protection device 1 (surge protection circuit 15), an overcurrent detection circuit 32, a cutoff switch 34, and a step-down power supply circuit 35 are connected in series in this order. In addition, a voltage detection circuit 33 is connected downstream of the overcurrent detection circuit 32 (between the overcurrent detection circuit 32 and the cutoff switch 34).

[0041] The DC-IN connector 31 is connected to a DC power supply such as an AC adapter as an external power source. The overcurrent detection circuit 32 detects large currents that flow when a short circuit or other problem occurs within the circuit board, and outputs an abnormality notification signal to the cutoff switch 34 when a large current is detected. The voltage detection circuit 33 detects overvoltages (steady overvoltages) and low voltages, and outputs an abnormality notification signal to the cutoff switch 34 when an overvoltage or low voltage is detected. The cutoff switch 34 is a path cutoff switch for protecting downstream electronic components 16 (e.g., an imaging element) and the like, and turns off when an abnormality notification signal is input. The step-down power supply circuit 35 reduces the voltage input from the DC-IN connector 31 to a voltage usable by the downstream electronic components 16. The overcurrent protection circuit corresponds to the overcurrent detection circuit 32 and the cutoff switch 34, and the overvoltage protection circuit corresponds to the voltage detection circuit 33 and the cutoff switch 34.

[0042] Even with the imaging device 30 configured as described above, when a surge voltage is input from the DC-IN connector 31, the surge protection circuit 15 can clamp the voltage to a clamp voltage. Furthermore, when a steady overvoltage is input from the DC-IN connector 31, the voltage detection circuit 33 and the cutoff switch 34 can protect the electronic components 16 from the overvoltage, and the capacitor 22 and resistor 23 can prevent thermal destruction of the clamp element 21 due to the overvoltage.

[0043] 7 is a diagram showing the configuration of the input section of the imaging device 40 of the second example. Note that the same components in the imaging device 40 of the second example and the imaging device 30 of the first example are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0044] 7, the imaging device 40 of the second example includes, in addition to the imaging device 30 of the first example, a protection device 1 (surge protection circuit 15), a battery connector 41, and a power supply switching circuit 42. The voltage detection circuit 33, the cutoff switch 34, and the power supply switching circuit 42 may be configured as a single integrated circuit.

[0045] In the imaging device 40, the DC-IN connector 31, one protection device 1 (surge protection circuit 15), overcurrent detection circuit 32, power supply switching circuit 42, cutoff switch 34, and step-down power supply circuit 35 are connected in series in this order. Also in the imaging device 40, the battery connector 41 and the other protection device 1 (surge protection circuit 15) are connected between the overcurrent detection circuit 32 and the power supply switching circuit 42. Also, the voltage detection circuit 33 is connected downstream of the power supply switching circuit 42 (between the power supply switching circuit 42 and the cutoff switch 34).

[0046] A battery as an external power source is connected to the battery connector 41. The power source switching circuit 42 is a circuit that selects between a DC power source and a battery power source as a power supply source.

[0047] Even in the imaging device 40 configured as described above, when a surge voltage is input from the DC-IN connector 31 or the battery connector 41, the surge protection circuit 15 can clamp the voltage to a clamp voltage. Furthermore, when a steady overvoltage is input from the DC-IN connector 31 or the battery connector 41, the voltage detection circuit 33 and the cutoff switch 34 can protect the electronic components 16 from the overvoltage, and the capacitor 22 and the resistor 23 can reduce thermal damage to the clamp element 21 due to the overvoltage.

[0048] 3. Modifications Note that the embodiment is not limited to the specific example described above, and various modified configurations may be adopted. For example, the protection device 1 has been described as being used in the image capture devices 30 and 40. However, the protection device 1 may be used in various devices to which a surge voltage may be input. For example, the protection device 1 may be used in an ECU (Electronic Control Unit) mounted on a vehicle.

[0049] In the above embodiment, the case where one capacitor 22 and one resistor 23 are provided has been described. However, a plurality of capacitors 22 and a plurality of resistors 23 may be connected in parallel.

[0050] 4. Summary of the Embodiment As described above, the protection device 1 according to the embodiment includes the clamp element 21 connected to the high-voltage line 4, the capacitor 22 connected between the clamp element 21 and the low-voltage line 5, and the resistor 23 connected in parallel with the capacitor 22 between the clamp element 21 and the low-voltage line 5. As a result, when an instantaneous surge voltage is input, charge is stored in the capacitor 22, causing a current to flow through the clamp element 21 and limiting the voltage of the high-voltage line 4 to the clamp voltage, and when a steady-state overvoltage is input, charge is stored in the capacitor 22, making it difficult for electricity to flow through the clamp element 21. Therefore, the protection device 1 can suppress damage to the clamp element 21, which is provided for protection against surge voltages, from steady-state overvoltage with a simple configuration.

[0051] The clamp element 21 is a diode that flows current from the high-voltage line 4 to the low-voltage line 5 when the voltage difference between the high-voltage line 4 and the low-voltage line 5 exceeds the clamp voltage, thereby limiting the voltage of the high-voltage line 4 to the clamp voltage. Examples of the diode that can be used include a TVS diode and a Zener diode. Using these diodes for the clamp element 21 makes it possible to clamp the surge voltage with a simple configuration.

[0052] The capacitance of the capacitor 22 is larger than the amount of charge stored in the capacitor due to the current flowing from the clamp element when a surge voltage is input to the high-voltage line. This prevents a charge exceeding the capacitance of capacitor 22 from being input from clamp element 21 even when a surge voltage is input, and also prevents current from stopping flowing through clamp element 21.

[0053] The resistance value of resistor 23 is set so that a current that will not cause thermal damage to clamp element 21 flows through clamp element 21 when a steady voltage higher than the clamp voltage is input to high-voltage line 4. This makes it possible to prevent thermal damage to clamp element 21 even if a small amount of current flows through clamp element 21 after the charge stored in capacitor 22 has become a capacitance when a steady overvoltage is input.

[0054] The resistance value of the resistor is set to a value that allows the charge stored in the capacitor to be discharged, so that even if a surge voltage or a steady overvoltage is input, the charge in the capacitor 22 will eventually be discharged, making the surge protection circuit 15 usable repeatedly.

[0055] A plurality of voltage supply sources are provided for the high voltage line 4. In this way, even when a plurality of different supply sources are connected, it is possible to protect the electronic components 16 from surge voltages.

[0056] A plurality of capacitors 22 can be connected in parallel, which allows the capacitance to be adjusted to any desired value using a ready-made capacitor.

[0057] A plurality of resistors 23 can be connected in parallel, which allows the resistance value to be adjusted to any value using a ready-made resistor.

[0058] The clamp element 21, capacitor 22, and resistor 23 are connected closer to the power supply than the overvoltage protection circuit for steady-state overvoltages, which makes it possible to clamp a surge voltage further upstream when the surge voltage occurs.

[0059] The imaging device 30 includes a connector (DCIN connector 31) to which an external power supply is connected, a surge protection circuit 15 connected to the connector and protecting the circuit from surge voltage when a surge voltage is input from the connector, and an overvoltage protection circuit (voltage detection circuit 33, cut-off switch 34) connected to the surge protection circuit 15 and protecting the circuit from overvoltage when an overvoltage is input from the connector, and the surge protection circuit 15 includes a clamp element 21 connected to the high-voltage line 4, a capacitor 22 connected between the clamp element 21 and the low-voltage line 5, and a resistor 23 connected in parallel with the capacitor 22 between the clamp element 21 and the low-voltage line 5. With this configuration, the same effect as that of the protection device 1 can be obtained.

[0060] The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0061] <5. Present Technology> The present technology may also have the following configurations. (1) A protection device comprising: a clamp element connected to a high-voltage line; a capacitor connected between the clamp element and a low-voltage line; and a resistor connected in parallel with the capacitor between the clamp element and the low-voltage line. (2) The protection device described in (1), wherein the clamp element is a diode that flows a current from the high-voltage line to the low-voltage line when a voltage difference between the high-voltage line and the low-voltage line becomes equal to or greater than a clamp voltage, thereby limiting the voltage of the high-voltage line to the clamp voltage. (3) The protection device described in (1) or (2), wherein the capacitance of the capacitor is greater than the amount of charge stored in the capacitor by the current flowing from the clamp element when a surge voltage is input to the high-voltage line. (4) The protection device described in any of (1) to (3), wherein the resistance value of the resistor is set so that a current flowing through the clamp element will not cause thermal damage to the clamp element when a steady voltage higher than the clamp voltage is input to the high-voltage line. (5) The protection device according to any one of (1) to (4), wherein the resistance value of the resistor is set to a value that allows the charge stored in the capacitor to be discharged. (6) The protection device according to any one of (1) to (5), wherein a plurality of voltage supply sources are provided for the high voltage line. (7) The protection device according to any one of (1) to (6), wherein a plurality of the capacitors can be connected in parallel. (8) The protection device according to any one of (1) to (7), wherein a plurality of the resistors can be connected in parallel. (9) The protection device according to any one of (1) to (8), wherein the clamp element, the capacitor, and the resistor are connected closer to the supply source than an overvoltage protection circuit for steady overvoltage.(10) An imaging device comprising: a connector to which an external power supply is connected; a surge protection circuit connected to the connector and protecting a circuit from a surge voltage when the surge voltage is input from the connector; and an overvoltage protection circuit connected to the surge protection circuit and protecting the circuit from an overvoltage when a steady overvoltage is input from the connector, wherein the surge protection circuit comprises: a clamp element connected to a high voltage line; a capacitor connected between the clamp element and a low voltage line; and a resistor connected in parallel with the capacitor between the clamp element and the low voltage line.

[0062] 1 Protection device 15 Surge protection circuit 21 Clamp element 22 Capacitor 23 Resistor

Claims

1. A protection device comprising: a clamp element connected to a high voltage line; a capacitor connected between the clamp element and a low voltage line; and a resistor connected in parallel with the capacitor between the clamp element and the low voltage line.

2. The protection device according to claim 1, wherein the clamp element is a diode that flows a current from the high voltage line to the low voltage line when the voltage difference between the high voltage line and the low voltage line becomes equal to or exceeds a clamp voltage, thereby limiting the voltage of the high voltage line to the clamp voltage.

3. The protection device according to claim 1, wherein the capacitance of the capacitor is greater than the amount of charge stored in the capacitor due to the current flowing from the clamp element when a surge voltage is input to the high voltage line.

4. The protection device according to claim 1, wherein the resistance value of the resistor is set so that a current that does not cause thermal damage to the clamp element flows through the clamp element when a steady voltage higher than a clamp voltage is input to the high voltage line.

5. The protection device according to claim 1, wherein the resistance of the resistor is set to a value that enables the charge stored in the capacitor to be discharged.

6. The protection device according to claim 1, wherein a plurality of sources of voltage supply to the high voltage line are provided.

7. The protection device according to claim 1, wherein a plurality of the capacitors can be connected in parallel.

8. The protection device according to claim 1, wherein a plurality of the resistors can be connected in parallel.

9. The protection device according to claim 1, wherein the clamp element, the capacitor and the resistor are connected closer to the supply source than an overvoltage protection circuit for steady-state overvoltages.

10. An imaging device comprising: a connector to which an external power source is connected; a surge protection circuit connected to the connector and protecting a circuit from a surge voltage when the surge voltage is input from the connector; and an overvoltage protection circuit connected to the surge protection circuit and protecting the circuit from the overvoltage when a steady overvoltage is input from the connector, wherein the surge protection circuit comprises: a clamp element connected to a high voltage line; a capacitor connected between the clamp element and a low voltage line; and a resistor connected in parallel with the capacitor between the clamp element and the low voltage line.